slice thickness .vs. slice separation .vs. interslice distance
Ana
The title says it all. Can some one please help me define the above terms
accuratly.
Regards,
Ana
--
Peter Clinch
> The title says it all. Can some one please help me define the above terms
> accuratly.
Subject to confirmation from more knowledgeable sources, slice thickness
would be the distance up/down the section for which a pixel in the slice
can be considered representative.
Slice separation and interslice distance would be one of the distance
between slice centres and the "dead space" not represented by pixels
between slices, but I'm not sure which is which...
Pete.
--
Peter Clinch University of Dundee
Tel 44 1382 660111 ext. 33637 Medical Physics, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net p.j.c...@dundee.ac.uk http://www.dundee.ac.uk/~pjclinch/
David Clunie
> Ana wrote:
> > The title says it all. Can some one please help me define the above terms
> > accuratly.
>
> Subject to confirmation from more knowledgeable sources, slice thickness
> would be the distance up/down the section for which a pixel in the slice
> can be considered representative.
> Slice separation and interslice distance would be one of the distance
> between slice centres and the "dead space" not represented by pixels
> between slices, but I'm not sure which is which...
>
> Pete.
(0018,0050) Slice Thickness is an attribute of an individual slice, and
it is the nominal slice thickness in mm of the reconstructed image. It
is the distance spanned by the slice in the axis normal to the plane of
the slice, i.e. one half of which is on one side of the slice center
and one half of which is on the other. It is a nominal value since in
reality, as a consequence of the manner of acquisition and reconstruction
of the data, it may vary across the area covered by the slice. It is an
attribute shared between the images using the Image Plane Module (i.e.
CT and MR). It is mandatory (i.e. always present).
(0018,0088) Spacing Between Slices is only present in MR (it is
not present in the CT image) and is defined to be the spacing
measured from the center-to-center of each slice.
However it is problematic in that spacing is an attribute of two
related slices and cannot really be encoded in a single image;
i.e. what value would be here in contiguous slices if the spacing
changed ? This doesn't happen very often in MR but is potentially
problematic. It is also an optional attribute and may not be present.
The safest way to find the spacing between slices is to ignore this
attribute completely and derive a value from the Image Position
(Patient) and Image Orientation (Patient) given two slices that
one needs to determine the spacing between.
The computed or encoded spacing between slices may be less than
the nominal slice thickness when slices "overlap." It may be
greater than the slice thickness if there is a "gap" between
slices.
Also be aware that there are buggy modalities that write the
wrong value in (0018,0088) Spacing Between Slices, sending the
spacing between the adjacent edges of slices rather between
centers.
david